What Causes Delayed Periods And Negative Pregnancy Test?

my fiancee and me had a four play, we dint involved in intercourse but she is not getting her periods, her last period was june 13th itseems, generally for her periods delay one week, now more than one week over, i have done pregnency test with kit, it was negative, yesterday doctor gave gynaset 5mg tablet, please suggest are we out of pregnancy ?we don t want that now